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Full text of "Text Book Of Mechanical Engineering"

Taps.

and Dies for bolts or spindles, and taps for the nuts in which
these spindles are to fit. Taps are made in "sets of three to
each diameter of screw, and to cut V threads of * Whitworth '
pitch; that is, whose pitch per diameter agrees with those in the
table devised by Sir Joseph Whitworth, .and which is here
appended:

V Threaded Screws (Whitworth).

Dia.
 in ins.
	Threads per inch.
 24
	Dia.    ' Threads in ins.     per inch.
	Dia.    ! Threads in ins,    ;. per inch.
	Dia.
 in ins.
 4}
	Threads per inch.
 *H?       '

TV
		i          8
	2i   \   4
		
i
	20
	4        7
	4    i    4
	4f
	s- !

TF
	18
	ti   .   7
	**    i    3
	5
	2-

;j
 "S"
	16
	if        6
	3          3l
	sl-
	& ;

TF
	14
	4        6
	3i        3l
	Si
	-s-

i
	12
	if       5
	3*        3*
	5f
	2-?r

1
	II
	if        5
	3f        3
	6
	2-|

f
	I 0
	.   ij        4i
	4          3
	
	

7
 F
	.    9
	2    i  4
	4i         4
	
	

Very rarely are taps used beyond i^ ins. diameter, larger sizes
being screwed in the lathe. The set of three is shewn at Fig, 205,
and includes 'taper7 (A), 6middle' (B), and 'plug' taps (c).

These are made by forming in the lathe a perfect screw thread
upon a f blank/ and afterwards fluting to the section shewn
enlarged at E, so that when the tap is turned right-handed it has
a cutting angle of 90, and a small relief or clearance angle,
removed with the file. Next, two-thirds of the length of the taper
tap, and one-third of the middle tap are turned off, after which
all are hardened as shewn at page 127. When in use the nut
must first be tapped, and the bolt afterwards screwed to fit it
After drilling to 'tapping size/ that is, to the diameter at the
bottom of the screw thread, the taper tap is first entered (while
the nut is held in the vice), and is turned round by a wrench D
applied to the square on the top. Only when turned right-
handed is the thread cut, a will be seen on reference to E,